1. Field of the Invention
This invention relates to a braze fixture and method of using, and has particular reference to the making of an all-brazed heat exchanger of a tube and header type.
2. Description of the Prior Art
Heat exchangers, especially those of compact, high performance design using fin material as a secondary heat transfer surface, are comprised of numerous parts some of which have a thin, light-weight construction. Manufacturing techniques have been developed according to which parts are formed, assembled, and the assembled unit placed into a holding fixture, and, while so held, subjected to a brazing operation, as for example by being heated in a furnace until applied braze alloy or braze material melts and flows to form a seal and a bond at all assembly joints. In a single operation, therefore, the heat exchanger parts are joined together by means acting not only as a seal and as a bond but also as a means promoting good heat transfer between the parts. In addition, joints are secure against damaging effects of temperature extremes and vibration.
As held in the braze fixture, it is important that parts defining the numerous joints be made to contact one another with a constant, uniformly applied pressure during a brazing cycle. Weakly brazed or unbrazed joints can lead to failure of a unit in use or at least to below specification performance. One result of this requirement is that it is usually attempted to braze together in a single operation only core elements of the heat exchanger, with external features such as manifold members and in-out fittings added in a separate operation or operations. In particular, and since the fixturing would involve the simultaneous application of opposing pressures, there has been no attempt, to our knowledge, to braze manifold members to a header plate while at the same time the header plate is brazed to turned over tube ends.